Athletic performance monitoring system utilizing heart rate information

ABSTRACT

An illumination source may be configured to illuminate the skin of the user. An illumination detector may detect electromagnetic radiation reflected of the skin of the user. A compensation module may be configured to determine the position of the skin of the user relative to the illumination detector. A processor may be configured to determine a heart rate of the user by analyzing information corresponding to an amount of the electromagnetic radiation detected by the illumination detector. The processor may also determine the heart rate of the user by compensating for the position of the skin of the user as determined by the compensation module.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/063,767 entitled “Athletic Performance Monitoring System UtilizingHeart Rate Information” and filed on Oct. 25, 2013, which claims thebenefit of U.S. Provisional Patent Application No. 61/719,172 entitled“Athletic Performance Monitoring System Utilizing Heart RateInformation” and filed on Oct. 26, 2012, which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The invention relates generally to athletic performance monitoringsystems, and more particularly, to such systems that utilize heart rateinformation.

BACKGROUND

Accurate heart rate measurements may improve the utility of wrist-worndevices that measure the movements and activities of a user and provideactivity points in response. For some work outs, the activity mayinvolve substantially static movements that work mainly against gravitybut are nonetheless strenuous. Examples include yoga, weight lifting,and other isometric exercises. Utilizing an accelerometer as the solesensing element for these types of activities may result in anunderestimating of the activity if the recorded movement is minimalcompared to other activities that involve larger movements such asrunning or dancing in which the heart rate is strongly associated withthe intensity of the movement. The addition of heart rate to theactivity estimation algorithms greatly improves the range of activitiesin which an accurate estimate of activity occurs.

When measuring heart rate for sports-related activities and other typesof activities, it is desirable that the heart rate sensor is portableand non-invasive. Existing technologies that may be used to measureheart rate, such as electrocardiography (ECG), may not be suited forsome types of activities. Although some existing technologies to measureheart rate have been incorporated into devices that may be worn by auser, these existing technologies may require a user to actively selecta button at the device to initiate the heart rate measurement. Moreover,existing device that may be worn by a user may require the device to bein intimate contact with the skin of the user in order to perform anaccurate heart rate measurement. Such requirements may not be feasiblein order to measure the heart rate of a user contemporaneous withperformance of an activity by the user. In addition, existing devicesthat may be worn by users, such as a chest strap may be uncomfortable.

A full discussion of the features and advantages of the presentinvention is deferred to the following detailed description, whichproceeds with reference to the accompanying drawings.

SUMMARY

The following presents a general summary of aspects of the invention inorder to provide a basic understanding of at least some of its aspects.This summary is not an extensive overview of the invention. It is notintended to identify key or critical elements of the invention or todelineate the scope of the invention. The following summary merelypresents some concepts of the invention in a general form as a preludeto the more detailed description provided below.

A first aspect described herein provides a method of determining heartrate. The skin of a user may be illuminated with an illumination source.An illumination detector may detect electromagnetic radiation reflectedoff the skin of the user. The position of the skin relative to theillumination detector may be determined based on the electromagneticradiation reflected. A processor may determine a heart rate of the userby analyzing information corresponding to the electromagnetic radiationreflected and compensating for the position of the skin of the user.

A second aspect described herein provides a heart rate determinationsystem. An illumination source may be configured to illuminate the skinof the user. An illumination detector may detect electromagneticradiation reflected of the skin of the user. A compensation module maybe configured to determine the position of the skin of the user relativeto the illumination detector. A processor may be configured to determinea heart rate of the user by analyzing information corresponding to anamount of the electromagnetic radiation detected by the illuminationdetector. The processor may also determine the heart rate of the user bycompensating for the position of the skin of the user as determined bythe compensation module.

A third aspect described herein provides an optical detector. Theoptical detector may include two illumination modules positionedorthogonally relative to one another. Each illumination module mayinclude a near-field LED and a far-field LED. The LEDs may be configuredto provide infrared illumination. An illumination detector may include aphotodiode that is configured to detect an amount of IR radiationreflected of the skin of a user. The photodiode may be offset from atleast one of the centerlines of the optical detection module. Aninterface may be configured to provide information corresponding to theamount of IR illumination reflected off the skin of the user.

These aspects and additional aspects will be appreciated with thebenefit of the detailed described provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example implementations are illustrated by way of example, and notby way of limitation, in the figures of the accompanying drawings and inwhich like reference numerals refer to similar elements.

FIG. 1 is a block diagram of an example of an implementation of a heartrate monitor in accordance with various aspects of the presentdisclosure.

FIG. 2 is a block diagram of an example of an implementation of adetection module of a heart rate monitor in accordance with variousaspects of the present disclosure.

FIG. 3A is a plan view of an example of an implementation of a detectionmodule of a heart rate monitor.

FIG. 3B is a front side view of the detection module of FIG. 3A.

FIG. 3C is a lateral side view of the detection module of FIG. 3A.

FIG. 4A is a lateral side view of the detection module of FIG. 3Apositioned relative to the skin of an individual.

FIG. 4B is another lateral side view of the detection module of FIG. 3Apositioned relative to the skin of an individual.

FIG. 5 is a flowchart of example method steps for determining a heartrate using a heart rate monitor.

FIG. 6 is another flowchart of example method steps for determining aheart rate using a heart rate monitor.

FIG. 7A is a perspective view of another example of an implementation ofa detection module of a heart rate monitor.

FIG. 7B is another perspective view of the detection module of FIG. 7A.

FIG. 7C is an additional perspective view of the detection module ofFIG. 7A.

FIG. 8 is a perspective view of an example of an implementation of adevice that may incorporate a heart rate monitor.

FIG. 9 is block diagram of an example of an implementation of a systemfor monitoring the movements of a user.

FIG. 10 is a block diagram of an example of an implementation of acomputer of the system of FIG. 9.

FIG. 11 is an illustration of example locations on the body of the userwhere sensors may be located to measure the movements of the user.

DETAILED DESCRIPTION

A heart rate monitor is provided that may be worn by an individual, andthe heart rate monitor may, in operation, determine a heart rate for theindividual. According to some aspects of the disclosure, the heart ratemonitor may be an optical heart rate monitor that measures heart ratebased on the scattering of light through the skin of the individual asblood flows beneath the skin. The scattering of light through the skinof the individual may depend on whether blood is or is not presentbeneath the skin. Accordingly, the scattering of light through the skinof the individual may change as blood flows beneath the skin due to theheart beat of the individual. The optical heart rate monitor may detectthe change in the scattering of light and determine a heart rate for theindividual based on this change. The optical heart rate monitor mayfunction over a broad range of illumination intensities and in a varietyof ambient lighting conditions.

It will be appreciated, however, that the position of the skin of theindividual may change beneath an optical heart rate monitor worn by thatindividual as the individual moves. As a result, the position of theskin relative to the optical heart rate monitor may affect the opticalinput received at the optical heart rate monitor. Accordingly, accurateheart rate measurements may be obtained by compensating for the skinposition of the individual when obtaining optical input with which todetermine a heart rate for the individual. Compensating for the skinposition of the individual may be achieved by obtaining optical feedbackfrom the heart rate monitor.

The heart rate monitor uses photoplethysmographic techniques todetermine the heart rate of an individual. The advantage ofphotoplethysmography (PPG) is that it does not require anelectro-potential measurement on opposing sides of the heart (body). Itthus can be placed in the more desirable locations other than the chestsuch as, for example, on the upper or lower arm or wrist even within thedevice on the wrist.

PPG may, however, come with its own set of challenges. The firstchallenge may relate to providing a device, such as a wrist-worn device,that is not uncomfortable to the wearer. A user may prefer a looser fitfor a device around the wrist. As a result, the spacing between thesensor of the device and the surface of the skin may vary, e.g., as thewearer moves. Where the device includes an optical sensor, the variationin spacing between the device and the skin of the user may modulate thereflected light in manner similar to the spectral scattering thatmodulates the light due to the heart beat of the wearer. To address thischallenge, a device may be designed such that the sensor is held firmlyagainst the skin of the wearer when the device is worn.

The second challenge may relate to the variation caused by the movementof the wearer. Even with the sensor held firmly against the skin,variations unrelated to heart rate may appear in the measurement. Thisvariation may result from the relative angle changes between theimpinging light and the skin surface as the muscles underlying lift andtwist the device. Mean changes in blood pressure may also shift thesignal with motion. Local variation in skin pigmentation can move in andout of the field of view of the sensor during activity. All of thesemovement-induced sources of noise may require compensation in order toidentify the variation in light that is solely the result of theheartbeat of the wearer.

The heart rate monitor described below performs motion compensation inorder to lower the movement-induced noise and provide an accuratedetermination of heart rate. The heart rate monitor described below mayalso be configured such that it may be used with a “comfort fit” (asmost people wear their watches), which may be preferable to an “elasticband” fit, which may hold the a sensor tight against the skin of thewearer as in exiting technologies.

The functional details of the heart rate monitor, including detailsdirected towards compensating for the skin position of the individual,are provided below. Stated generally, some example implementations ofthe heart rate monitor may provide one or more light emitting diodes,photodiodes, amplifiers, integrating analog-to-digital converters(ADCs), accumulators, clocks, buffers, comparators, a state machine, anda bus interface. The photodiode may be responsive to electromagneticradiation such as, e.g., infrared light. An integrating ADC may convertan amplified photodiode current into a digital signal. Upon completionof a conversion cycle, the conversion result may be transferred to adata register. The result may thus represent an amount ofelectromagnetic radiation reflected off the skin of the user anddetected at the photodiode. The digital output may be read by amicroprocessor through which motion compensation may be appliedresulting in an approximate heart rate for an individual.

In the following description of various example implementations,reference is made to the accompanying drawings, which form a parthereof, and in which are shown by way of illustration various exampledevices, systems, and environments in which aspects of the disclosuremay be practiced. It is to be understood that other specificarrangements of parts, example devices, systems, and environments may beutilized and that structural and functional modifications may be madewithout departing from the scope of the present disclosure. Also, whilethe terms “top,” “bottom,” “front,” “back,” “side,” and the like may beused in this specification to describe various example features andelements, these terms are used herein as a matter of convenience, e.g.,based on the example orientations shown in the figures. Nothing in thisspecification should be construed as requiring a specific threedimensional orientation of structures in order to fall within the scopeof the disclosure. Moreover, various aspects of the disclosure may beimplemented using instructions stored on computer-readable media. Asused in this disclosure, computer-readable media includes allcomputer-readable media with the sole exception being a transitorypropagating signal.

In FIG. 1 a block diagram of an example of an implementation of a heartrate monitor 100 in accordance with various aspects of the presentdisclosure is shown. The heart rate monitor 100, in this example,includes a detection module 102; a compensation module 104; a heart ratedetermination module 106; a compensation factor lookup table 108; andmemory storing device calibration information 110. The detection module102, in this example, includes a detector 112 and a source module 114.The source module 114, in this example, includes a near-field source 116and a far-field source 118. As discussed in further detail below, adetection module of a heart rate monitor may include multiple sourcemodules where each source module respectively includes a near-fieldsource and a far-field source.

The near-field source 116 and the far-field source 118 may be, in someexample implementations, light-emitting diodes. In other exampleimplementations, the near-field source 116 and the far-field source 118may be implemented using alternative types devices that generateelectromagnet radiation. The electromagnetic radiation may be, forexample, in the visible or infrared (IR) spectrum. In further exampleimplementations, the near-field source 116 and the far-field source 118may be implemented using devices that generate acoustic waves or otherforms of energy suitable to monitor heart rate or determine a distanceof a device from a surface, such as the distance between a wrist-worndevice and the wrist of an individual wearing the wrist-worn device.

The compensation module 104 may identify a compensation factor to usewhen determining a heart rate for an individual. As described in furtherdetail below, the compensation module 104 may identify a compensationfactor based upon one or more ratios calculated from the output of thedetector 112 of the detection module 102. The compensation factor lookuptable 108 may store the compensation factors. The compensation factorsstored in the compensation factor lookup table 108 may respectivelycorrespond to a particular position of the skin of the user wearing theheart rate monitor 100. As described in further detail below, thecompensation factors of the compensation factor lookup table 108 may beassociated with one or more count value ratios. The compensation module104 may perform a lookup of the compensation factor lookup table 108using one or more count value ratios. The compensation module 104 maythus retrieve the compensation factor of the compensation factor lookuptable 108 that is associated with the one or more count value ratiosprovided. Count value ratios will be discussed in further detail below.

The compensation factor may be applied when determining a heart rate inorder to compensate for the skin position of an individual wearing theheart rate monitor 100. In some example implementations, thecompensation module 104 may apply the compensation factor to the outputof the detector 112 of the detection module 102. Alternatively, in otherexample implementations, the compensation module 104 may provide thecompensation factor to the heart rate determination module 106, and theheart rate determination module may process the output received from thedetector 112 using the compensation factor in order to accuratelydetermine a heart rate for the individual. The heart rate determinationmodule 106 and the compensation module 104 may be implemented usinghardware, software, or a combination of hardware and software. In someexample embodiments, the heart rate determination module 106 and thecompensation module 104 may be implemented using a microprocessorprogrammed to perform one or more of the functions described below. Theheart rate monitor 100 may also include a controller (not shown) suchas, e.g., a microprocessor. As discussed further below, themicroprocessor may be used to determine the heart rate of theindividual.

In FIG. 2, a block diagram of an example of an implementation of adetection module 200 of a heart rate monitor (e.g., heart rate monitor100 of FIG. 1) in accordance with various aspects of the presentdisclosure is shown. The detection module 200, in this example, includesa detector 202 and two source modules 204 a and 204 b. The detector 202,in this example, includes an illumination sensor 206, a gain control208, an analog-to-digital converter 210, a data register 212, a memory214, and a bus interface 216. The source modules 204 a and 204 b mayeach include two illumination sources, a near-field illumination sourceand a far-field illumination source. In FIG. 2, for example, the sourcemodule 204 a includes a near-field illumination source 218 a and afar-field illumination source 220 a, and the source module 204 bincludes a near-field illumination source 218 b and a far-fieldillumination source 220 b.

In some example implementations, the near-field illumination sources 218a-b and far-field illumination sources 220 a-b may be light-emittingdiodes (LEDs). Accordingly, the near-field illumination sources 218 a-bmay be referred to as near-field LEDs, and the far-field illuminationsources 220 a-b may be referred to as far-field LEDs. The near-fieldLEDs 218 a-b may be utilized to illuminate the skin of an individualwearing the device when the skin is positioned relatively close to thedetector 202, e.g., when the skin of the individual is in the near-fieldregion. The far-field LEDs 220 a-b may be utilized to illuminate theskin of the individual when the skin is positioned relatively far fromthe detector 202, e.g., when the skin of the individual is in thefar-field region. The near-field LEDs 218 a-b and the far-field LEDs 220a-b may be configured to emit IR illumination.

The anodes of the LEDs 218 a-b and 220 a-b may be individually connectedto a voltage source such that each LED is individually drivable from itsrespective voltage source (not shown). The cathodes of the LEDs 218 a-band 220 a-b may be commonly connected to a current sink (not shown), andthe anodes of the LEDs may be individually connected to general purposeinput/output pins of a microprocessor (not shown), which mayindividually drive the LEDs.

The illumination sensor such as the illumination sensor 206 may, in someexample implementations, be a photodiode that detects illumination fromthe near-field LEDs 218 a-b and far-field LEDs 220 a-b. The illuminationdetected by the photodiode 206 may include illumination that reflectsoff the skin of an individual. As the near-field LEDs 218 a-b andfar-field LEDs 220 a-b may be configured to emit IR illumination, thephotodiode 206 may be configured to detect the IR illumination. Thephotodiode 206, due to its construction, may be responsive to both IRillumination and illumination in the wavelength range of visible light.It has been observed that ambient visible light superimposed with IRillumination may include frequency spectra similar to that of the bulkscatter of light during a heartbeat. In order to combat this effect, thedetector 202 may include an optical filter that blocks illumination inthe wavelength range of visible light. As a result, the photodiode 206may receive the IR illumination and not receive the visible light. Thephotodiode 206 may convert the IR illumination received into an analogcurrent signal. The photodiode 206 may provide the analog current signalto the ADC 210

The ADC 210 may be an integrating ADC that converts the analog currentsignal received from the photodiode 206 into a digital output. When theLEDs 218 a-b or 220 a-b are illuminated, the integration may beinitiated. upon completion of the conversion cycle, the output of theADC may be stored in the data register 212, and the LEDs may bedeactivated. The analog current signal received from the photodiode 206may be amplified before converting the analog signal into a digitaloutput. The data register 212 may store the value of the digital output.To ensure data integrity, transfers to the data register 212 may bedouble-buffered.

The digital output value may be read from the data register 212 via thebus interface 216 and provided to, e.g., a microprocessor of the heartrate monitor. The photodiode 206 may be referred to as a channel, andthe output of the photodiode may be referred to as a channel count. Theanalog current signal provided by the photodiode 206 may correspond tothe channel count, and the analog current signal may be converted into adigital value by the ADC 210 and stored at the data register 212.

The ADC 210 may provide digital output having up to 16 bits ofresolution, and the integration time may impact both the resolution andthe sensitivity of the reading from the photodiode 206. The integrationtime for one integration cycle may be 136 microseconds (μs).Additionally, the ADC 210 may be configured to perform up to 256integration cycles.

The gain control 208 may control the amount of gain of the currentsignal from the photodiode 206. The gain control 208 may be programmedto provide gain of, e.g., 1×, 8×, 16×, or 120×. The memory 214 may be,e.g., flash memory and store manufacturing information and calibrationinformation such as the device calibration information 110 discussedabove with reference to FIG. 1. A microprocessor may access theinformation stored at the memory 214 via the bus interface 216.

The bus interface 216 may be, e.g., an I²C serial-compatible interface,standard or fast mode that access a set of registers (not shown) of theheart rate monitor. The I²C bus may be available from NXP SemiconductorsN.V. headquartered in Eindhoven, The Netherlands. Additional andalternative types of busses and protocols may be selectively employed.

The registers may provide access to control functions and output data ofthe heart rate monitor. Some examples of the various registers that theheart rate monitor may provide include a command register; an enableregister; an integration time register; a wait time register; aconfiguration register; a gain control register; an identificationregister; a status register; one or more data registers. The commandregister may specify the address of a target register for read or writeoperations. The enable register may be utilized to power the heart ratemonitor on and off and enable various functions of the heart ratemonitor. The enable register may, for example, be utilized to power on(PON) the heart rate monitor, enable the ADC 210 (AEN) of the heart ratemonitor, and enable a wait timer (WEN) of the heart rate monitor thatput the heart rate monitor into a wait state. The integration timeregister may be used to control the integration time of the ADC 210,e.g., in 136 μs increments. Accordingly, the integration time registermay store a value corresponding to a desired number of integrationcycles. The wait time register may store a wait time also in 136 μsincrements, and the wait time register may store a value correspondingto a desired number of wait time increments.

The configuration register may store information used to scale the gainlevel and the wait time. Depending on the value stored in theconfiguration register, the gain level may, for example, be scaled by afactor of 0.16 or by a factor of 1. Also depending on the value storedin the configuration register, the wait time increment may be scaled bya factor of 12. The gain control register may provide a selected amountof gain to the ADC 210 of the heart rate monitor. The identificationregister may provide one or more values corresponding to a part numberof the heart rate monitor. The status register may provide informationregarding the internal status of the heart rate monitor. The statusregister may, for example, store a value corresponding to a cyclicredundancy check, which may be compared when writing information tomemory of the heart rate monitor in order to determine validity of theinformation. The status register may also store a value that indicatesthe ADC 210 of the heart rate monitor has completed an integrationcycle. The data register of the heart rate monitor, e.g., data register212, may store the digital output from the ADC 210 as described above.The digital output provided by the ADC 210 may be stored in a dataregister as a 16-bit value. In some example implementations, multipledata registers may be employed, e.g., two data registers that store thedigital output as two 16-bit values.

The heart rate monitor may support low-power modes including a sleepstate, a wait state, and an active state. In the sleep state, only theresources used to detect a start condition at the bus interface 216 andused to check the enable register may be utilized. When the powermanagement feature is enabled, a state machine of the heart rate monitormay transition to the wait state. The wait time may be determined by thevalues of the wait time register and the configuration register asdescribed above. In the active state, the LEDs 218 a-n and 220 a-b maybe activated to provide illumination. Also in the active state, thephotodiode 206 may provide an analog current signal in response toillumination detected at the photodiode. Accordingly, the ADC 210 mayalso be activated in the active state in order to convert the analogcurrent signal provided by the photodiode 206 to a digital output asdescribed above. When the heart rate monitor is enabled, the statemachine may transition through an initialization process to the activestate. The time the heart rate monitor is in the active state may dependon the value stored in the integration time register.

An internal state machine may be utilized to control the active and waitfeatures of the heart rate monitor. At power up, an internalpower-on-reset may initialize the heart rate monitor and place the heartrate monitor in the low-power sleep state. When a start condition isdetected at the bus interface 216, the heart rate monitor may transitionto an idle state and check the enable register. If enable registerindicates the heart rate monitor is disabled, the heart rate monitor mayreturn to the sleep state to save power. Otherwise, the heart ratemonitor may remain in the idle state until the enable register indicatesthe heart rate monitor is enabled. Once enabled, the heart rate monitormay carry out the wait states and active states in sequence as describedabove. Upon completion of a cycle and return to the idle state, theheart rate monitor may automatically begin a new wait-active cycle aslong as the device remains powered on and enabled.

Referring now to FIGS. 3A-B, an illustration of another exampleimplementation of a detection module 300 of a heart rate monitor isshown. In FIG. 3A, a plan view of the detection module 300 of is shown.In FIG. 3B, a front side view of the detection module 300 is shown, andin FIG. 3C, a lateral side view of the detection module 300 is shown. InFIG. 3B and FIG. 3C, a cut-out of the detection module 300 isillustrated via respective dashed lines in order to illustrate variouscomponents of the detection module. It will be appreciated that theterms front side and lateral side are simply used for convenience andshould not be construed to identify any particular side of the detectionmodule 300.

The detection module 300 in FIGS. 3A-C may be similar to the detectionmodule 200 described above with reference to FIG. 2. Accordingly, thedetection module 300, in this example, includes an illumination sensor302 having a photodiode 304 and two illumination source modules 306 aand 306 b. The illumination source module 306 a may include a near-fieldLED 308 a and a far-field LED 310 a. The illumination source module 306b may likewise include a near-field LED 308 b and a far-field LED 310 b.The detection module 300 may also include respective lens elements thatcover the LEDs 308 a-b and 310 a-b as well as the photodiode 304. Thedetection module 300, in this example, may include a lens element 312athat covers LED 308 a, a lens element 312b that covers LED 310 a, a lenselement 312c that covers LED 308 b, and a lens element 312d that coversLED 310 b. The detection module 300 may also include a lens element 314that covers the photodiode 304. In addition, the detection module 300,in this example, may include a window 316 across the face of thedetection module that protects the various components of the detectionmodule. Lens elements will be discussed in further detail below.

As also shown by way of example in FIG. 3A, a centerline 318 of thephotodiode 304 along the Y-axis may be offset from the centerline 320 ofthe detection module 300 along the Y-axis. The centerline 322 of thephotodiode 304 along the X-axis, however, may be collinear with thecenterline 324 of the detection module 300 along the X-axis in thisexample. As also shown by way of example in FIG. 3A, the LEDs 308 a-band the LEDs 310 a-b are positioned at an oblique angle relative to thecenterlines 318 and 322 of the photodiode 304. The LEDs 308 a-b and 310a-b, in this example, are positioned at about a 45° angle relative tothe centerlines 318 and 322 of the photodiode 304. It will thus beappreciated that a line extending through LEDs 308 a and 310 a and aline extending through LEDs 308 b and 310 b and intersecting at thecenter of the photodiode 304 may be orthogonal relative to one another.

As seen in FIG. 3B and FIG. 3C, the detection module may have a width,w, a length, l, and a thickness, t. In some example implementations, thewidth, w, of the detection module 300 may be about 10 mm; the length, l,of the detection module may be about 12 mm; and the thickness, t, of thedetection module may be about 5 mm. It will be appreciated that thedimensions of the detection module 300 may depend on various designconstraints that arise during various implementations of the detectionmodule. Accordingly, alternative implementations of the detection modulemay exhibit alternative dimensions.

The face of the detection module 300 may be positioned against the skinof an individual when the individual wears a heart rate monitor thatincorporates the detection module. The position of the skin relative tothe face of the detection module 300 may be described in terms of atranslation, ΔZ, along the Z-axis; a rotation, θ_(X), of a surface ofthe skin about the X-axis; and a rotation, θ_(Y), of the surface skinabout the Y-axis. The translation, ΔZ, may represent the distancebetween the face of the detection module 300 and the surface of the skinof the individual wearing the heart rate monitor. When the face of thedetection module 300 is flat against the surface of the skin of theindividual, the skin position may be referred to as the origin skinposition and described as ΔZ=0, θ_(X)=0°, and θ_(Y)=0°. Whencompensating for the skin position during the heart rate determinationprocess, the skin position may be described relative to this origin skinposition. The range of translation of the surface of the skin along theZ-axis (the “Z range”) may, in some circumstances, range between about 0mm (Z_(min)) and about 8.6 mm (Z_(max)). In addition, the rotation ofthe surface of the skin about the X-axis, θ_(X), may range between about−19.6° and about +19.6°; and the rotation of the surface of the skinabout the Y-axis, θ_(Y), may range between about −31.4° and about+31.4°.

As described above, an accurate heart rate may be determined bycompensating for the changes in illumination caused by the changes inthe position of the skin of an individual as the individual moves whilewearing the heart rate monitor. The heart rate monitor may compensatefor the position of the skin of the individual by obtaining spatialfeedback regarding the position of the skin of the individual. Thespatial feedback may be obtained by measuring the ratio of therespective count values obtained when a near-field LED and a far-fieldLED of an illumination source module are illuminated, e.g., a countvalue, N, for the near-field LED 308 a and a count value, F, for thefar-field LED 310 a of illumination source module 306 a. A count valueratio, N/F, may be obtained for each of the source modules of adetection module, e.g., the source modules 306 a and 306 b of thedetection module 300.

It will be appreciated that the count value for an LED may depend on theposition of the surface of the skin of an individual wearing the heartrate monitor. Referring to FIGS. 4A-B, a lateral side view of thedetection module 300 relative to the skin 400 of an individual is shown.In FIG. 4A the skin 400 of the individual is relatively close to thedetection module 300. Stated differently, the translation of the skin400 along the Z-axis, ΔZ₁, is relatively small in FIG. 4A. In FIG. 4Bthe skin 400 of the individual is relatively far from the detectionmodule 300. Stated differently, the translation of the skin 400 alongthe Z-axis, ΔZ₂, is relatively large in FIG. 4B.

As seen in FIGS. 4A-B, the amount of illumination from the LEDs 308 band 310 b that is detected by the photodiode 304 may depend on theposition of the skin 400 relative to the detection module 300. As seenin FIG. 4A, for example, illumination from the near-field LED 308 b mayfall within the field-of-view (FOV) 402 of the photodiode 304 when theskin 400 is relatively close to the detection module 300, e.g., when ΔZ₁is relatively small. As also seen in FIG. 4A, most or all of theillumination from the far-field LED 310 b may fall outside of the FOV402 of the photodiode 304 when the skin 400 is relatively close to thedetection module.

As a result, the photodiode 304 may detect illumination from thenear-field LED 308 b that falls within the FOV 402 and is reflected offthe skin 400 when the skin is relatively close to the detection module300. The photodiode 304 might not, however, detect most or all of theillumination from the far-field LED 310 b that falls outside of the FOV402 when the skin 400 is relatively close to the detection module 300.It will thus be appreciated that the count value, N, for the near-fieldLED 308 b may be relatively high and the count value, F, for thefar-field LED 310 may be relatively low (e.g., close to zero) when theskin 400 is relatively close to the detection module 300. Accordingly,the count value ratio, N/F, may approach infinity (N/F→∞) as thedistance, ΔZ₁, between the detection module 300 and the skin 400decreases and the count value, F, for the far-field LED 310 b approacheszero.

When the skin 400 is relatively far from the detection module 300,however, the illumination from the far-field LED 310 b may fall withinthe FOV 402 of the photodiode 304 and illumination from the near-fieldLED 308 a may fall outside the FOV 402 of the photodiode. As seen inFIG. 4B, for example, illumination from the far-field LED 310 b may fallwithin the FOV 402 of the photodiode 304 when the skin 400 is relativelyfar from the detection module 300, e.g., when ΔZ₁ is relatively large.As also seen in FIG. 4B, most or all of the illumination from thenear-field LED 308 b may fall outside of the FOV 402 of the photodiode304 when the skin 400 is relatively far from the detection module.

As a result, the photodiode 304 may detect illumination from thefar-field LED 310 b that falls within the FOV 402 and is reflected offthe skin 400 when the skin is relatively far from the detection module300. The photodiode 304 might not, however, detect most or all of theillumination from the near-field LED 308 b that falls outside of the FOV402 when the skin 400 is relatively far from the detection module 300.It will thus be appreciated that the count value, N, for the near-fieldLED 308 b may be relatively low (e.g., close to zero) and the countvalue, F, for the far-field LED 310 may be relatively high when the skin400 is relatively far from the detection module 300. Accordingly, thecount value ratio, N/F, may approach zero (N/F→0) as the distance, ΔZ₁,between the detection module 300 and the skin 400 increases and thecount value, N, for the near-field LED 308 b approaches zero.

A count value ratio, N/F, may be calculated for each illumination sourcemodule of a detection module. With reference to the detection module 300described above, a first count value ratio, N₁/F₁, may be calculated forthe source module 306 a based on a count value, N₁, obtained forillumination from the near-field LED 308 a and a count value, F₁,obtained for illumination from the far-field LED 310 a. Similarly, asecond count value ratio, N₂/F₂, may be calculated for the source module306 b based on a count value, N₂, obtained for illumination from thenear-field LED 308 b and a count value, F₂, obtained for illuminationfrom the far-field LED 310 b. The compensation module (e.g.,compensation module 104) may thus use this pair of count value ratios,N₁/F₁ and N₂/F₂, to identify a skin position by performing a lookup in acompensation factor lookup table such as the compensation factor lookuptable 108 described above with reference to FIG. 1.

The optical design of the detection module 300 creates a modulation ofthe photocurrent that depends on the spatial orientation of thedetection module with respect to the surface of the skin of theindividual. When the surface of the skin is near the window 316, theillumination from the far-field LEDs 310 a-b is mostly or entirelyoutside the FOV 402 of the photodiode 304. The photocurrent provided bythe photodiode 304 would therefore be near zero when the surface of theskin is near the window 316. In contrast, the illumination from thenear-field LEDs 308 a-b would result in a relatively high value ofphotocurrent from the photodiode 304 when the surface of the skin isnear the window 316 since the illumination from the near-field LEDswould fall within the FOV 402 of the photodiode.

The photocurrent provided by a photodiode may also depend on therotation of the detection module with respect to the surface of the skinof the individual. In example implementations having a source moduleparallel to the X-axis, the amount of illumination detected at aphotodiode from this source module may remain constant as the detectionmodule is rotated about the X-axis. The amount of illumination detectedby the photodiode from the other source module, which may be positionedorthogonal to the X-axis, may decline rapidly as the rotation about theX-axis increases in magnitude. When the detection module is rotatedabout the Y-axis as similar effect may be observed for a source modulepositioned parallel with the Y-axis and a source module positionedorthogonal to the Y-axis. Compound rotation about the X-axis and theY-axis may produce a response that is a convolution of the illuminationfrom both source modules. Example implementations that includerespective source modules parallel to the X-axis and Y-axis arediscussed further below with reference to FIGS. 7A-C.

A heart rate monitor may obtain spatial feedback by measuring the ratioof the current values obtained using the near-field LED and far-fieldLED of each source module, in other words, by illuminating the LEDs ofthe left source module and the right source module. The near-field LEDand the far-field LED of a source module may illuminated one at a time.The ADC provides a count value corresponding to the current provided bythe photodiode. The count values may then be stored for furtherprocessing and analysis. Each of the measured values may be divided by areference value to obtain a normalized ratio. The denominator of thenormalized ratio may be the count value resulting from illumination byany one of the LEDs. The reference value may, in some exampleimplementations, be the photocurrent measured when two or more of theLEDs are illuminated. The reference value may, for example, be thecurrent measured when both near-field LEDs are simultaneouslyilluminated, N₁ and N₂. Using this example, the ratios may beN₁/(N₁+N₂), N₂/(N₁+N₂), F₁/(N₁+N₂), F₂/(N₁+N₂). Since the relationshipbetween intensity of the illumination may be linear with respect tophotocurrent, the ratio may be unaffected by the absolute level ofintensity of each LED.

The spatial feedback corresponding to the orientation of a detectionmodule with respect to the skin may be determined by comparing thecalculated ratio to ratios contained in a compensation lookup table asdescribed above. The ratios contained in the compensation lookup tablemay be equated directly to a known orientation. The sum of the leastsquare difference between the calculated ratio and the ratios containedin the compensation lookup table may be used to identify the orientationof the compensation lookup table that best matches the presentorientation of the detection module.

The raw signal for determining heart rate may come from two sources: thephotocurrent with each near-field LED illuminated (the “near signal”)and the photocurrent with each far-field LED illuminated (the “farsignal”). For each orientation contained in the compensation lookuptable, there may be a scaling factor for the near signal and the farsignals. The scaling factors may be derived by characterizing theaverage signal magnitude at a particular orientation and dividing it bythe average signal magnitude at a nominal orientation such as, e.g.,ΔZ=2.8 mm, θ_(X)=0, and θ_(Y)=0.

With the actual orientation of the detection module determined, thecount value measured for the near signal may be multiplied by anear-field scaling factor and then stored as a spatially-compensated rawdata value. Likewise the count value for the far signal may bemultiplied by a far-field scaling factor and then also stored as thespatially-compensated raw value.

The entire data sampling sequence of N₁; N₂; N₁ and N₂; F₁; F₂; and F₁and F₂ may be repeated about 30-128 times per second. To save power, thespatial compensation may only be applied at a much lower sample intervalwith only N₁, N₂, F₁, and F₂ being illuminated singularly once everyfour measurements of the samples from N₁ and N₂; and F₁ and F₂.

The spatial compensation may depend on spatial feedback from thedetection module and may represent only one aspect of the entirecompensation process for motion. Additional feedback provided byancillary sensors such as accelerometers or gyrometers may also beincorporated to further cancel motion-induced noise in the raw signals.

The particular positioning of the near-field LEDs and far-field LEDswithin a detection module may affect the sensitivity of the N/F ratio aswell as the Z range over which illumination from the LEDs falls withinthe FOV of a photodiode. It will be appreciated that the angle ofincidence of the illumination from the LEDs increases as the LEDs movefarther out from the photodiode. As the LEDs move farther out from thephotodiode, the sensitivity of the N/F ration may increase, but the Zrange may decrease. A suitable position for the near-field LEDs andfar-field LEDs relative to the photodiode may be one in whichillumination is provided over an identified Z range while retaining aresponse for the N/F ratio.

The lens elements that cover the :LEDs of the detection module may focusthe illumination provided by the LEDs such that the maximum amount ofreflected illumination is achieved at a particular distance, ΔZ, alongthe Z-axis. In some implementations, for example, a lens element for anear-field LED may focus illumination from the near-field LED such thatthe maximum amount of reflected illumination is achieved when ΔZ=2.8 mm,θ_(X)=0°, and θ_(Y)=0°. In some implementations, as another example, alens element for a far-field LED may focus illumination from the farfield LED such that the maximum amount of reflected illumination isachieved when ΔZ=5.6 mm, θ_(X)=0°, and θ_(Y)=0°. Furthermore, thenear-field LEDs and far-field LEDs may be positioned off-center relativeto their respective lens elements to produce an illuminationdistribution in which peak illumination occurs non-orthogonal relativeto the face of the detection module. Additional and alternativeconfigurations will be appreciated with the benefit of this disclosure.

It will also be appreciated with the benefit of this disclosure thatvarious tolerances for the components of a detection module may lead toslightly different N/F ratios from individual detection modules. As anexample, the placement tolerances of the LEDs, and the molding andpositioning tolerances of the lens elements may contribute to variationsin the N/F ratio at given distances, ΔZ_(n), along the Z-axis. Tocompensate for these variations across individual detection modules, aheart rate monitor may have its response measured during testing inorder to determine unique calibration information for the heart ratemonitor. The calibration information may be stored at the heart ratemonitor (e.g., as device calibration information 110) and utilized whendetermining the heart rate of an individual wearing the heart ratemonitor.

In some example implementations, more than one detector or photodiode.For example, multiple detectors may be positioned around a wrist-worndevice, and one of the detectors may be selected for measuring heartrate at a given time based upon the N/F ratio associated with thatdetector. For example, the detector associated with an N/F ratioindicating that detector is the closest detector to the skin may be usedto obtain the compensation factor used when determining the heart rate.Stated more generally, the detector associated with an N/F ratioindicating that detector is positioned such that it is likely to producea signal corresponding to the most accurate heart rate may be used. Thedetector selected may vary over time as the device moves.

For the purposes of illustration, two pairs of LEDs representingnear-field and far-field sources are shown. Additional LEDs may also beused as near-field and far-field sources. In some exampleimplementations, a single pair of LEDs may be used as the near-field andfar-field source. In some example implementations, the near-field andfar-field sources may be associated with multiple detectors. Forexample, a single pair of near-field and far-field sources may bepositioned between multiple detectors and used with those detectorssimultaneously or independently. Alternative implementations of theheart rate monitor may include other types of sensors for determiningskin position (e.g., distance) relative to the device. For example, atemperature sensor may be used in some example implementations.Accelerometers, gyrometers, and other types of sensors may be used tosense various parameters that may be used to obtain compensationfactors.

In FIG. 5, a flowchart 500 of example method steps for determining aheart rate using a heart rate monitor is shown. The heart ratedetermination process may be initiated (block 502), and the near-fieldLED may be activated (block 504). A count value, N, for the near-fieldLED may be obtained (block 506), e.g., using a photodiode and an ADC asdescribed above. The far-field LED may then be activated (block 508),and a count value, F, for the far-field LED may also be obtained (block510), e.g., using the photodiode and the ADC as also described above.The ratio of N to F, the N/F ratio, may be calculated (block 512), and alookup may be performed using the N/F ratio (block 514), e.g., at acompensation factor lookup table as described above. The compensationfactor may be provided to a heart rate determination module using thecompensation factor (block 516) in order to account for the position ofthe skin of the user. It will be appreciated that steps 504-512 may beperformed for each source module of the detection module of a heart ratemonitor.

In FIG. 6, another flowchart 600 of example method steps for determininga heart rate using a heart rate monitor is shown. As noted above,various tolerances in the manufacturing of the heart rate monitor mayresult in variable N/F ratios across individual heart rate monitors.Accordingly, a calibration process may identify calibration informationthat each heart rate monitor may utilize when determining a heart ratefor an individual. The calibration process may be initiated (block 602)for a heart rate monitor, and the response from the detector of thedetection module of the heart rate monitor may be measured (block 604).Based on the measured response from the detector, calibrationinformation may be obtained for the heart rate monitor (block 606). Thecalibration information may be stored in non-volatile memory of theheart rate monitor (block 608), and the heart rate determination moduleof the heart rate monitor may apply the calibration information whendetermining a heart rate for an individual (block 610).

In FIGS. 7A-C, a perspective view of another example of animplementation of a detection module 700 of a heart rate monitor isshown. The detection module 700 may include features similar to that ofthe detection module 300 described above with reference to FIGS. 3A-C.The detection module 700 in this example, however, illustrates analternative configuration for the illumination detector 702 and thesource modules 704 a and 704 b. The source modules 704 a and 704 b maylikewise include a respective near-field illumination source 706 a and706 b and a respective far-field illumination source 708 a and 708 b. Asshown by way of example in FIG. 7A, the illumination detector 702 may bea photodiode, and the illumination sources 706 a-b and 708 a-b may beLEDs. The detection module 700 may also include a controller 710, e.g.,a microprocessor. The photodiode 702 and the LEDs 706 a-b and 708 a-bmay be connected to the microprocessor 710 as described above.Additionally, the microprocessor 710, photodiode 702, and LEDs 706 a-band 708 a-b may be positioned on a substrate 712 of the detection module700.

As seen in FIG. 7A, the photodiode 702 is positioned off-center of thesubstrate 712 proximate to one of the corners of the substrate. Thesource modules 704 a and 704 b, in this example, are positioned in linewith the photodiode 702 and orthogonal relative to one another. As shownin FIG. 7A, a centerline 714 passing through the source module 704 aintersects a centerline 716 passing through the source module 704 b atthe center of the photodiode 702 such that the centerlines 714 and 716are perpendicular relative to one another. As noted above, the LEDs maybe configured to provide IR illumination or visible light illumination.Accordingly, in some example implementations, the LEDs may exhibit apeak wavelength of around 590 nanometers (nm), which corresponds toamber-colored visible light. In other example implementations, the LEDsmay exhibit other wavelengths such as, e.g., around 560 nm, whichcorresponds to green-colored visible light.

As noted above, respective lens elements may cover the illuminationdetector and the illumination sources. Referring to FIG. 7B, thedetection module 700 may include multiple lens components 718 and 720a-b. The lens component 718 may cover the photodiode 702 and include alens element 722. The lens component 720 a may cover the illuminationsource module 704 a and include lens elements 724 a and 724 b. The lenselement 724 a may cover the near-field LED 706 a, and the lens element724 b may cover the far-field LED 708 a. Similarly, the lens component720 b may cover the source module 704 b and include lens elements 724 cand 724 d. The lens element 724 c may cover the near-field LED 706 b,and the lens element 724 d may cover the far-field LED 708 b.

As shown by way of example in FIG. 7B, the lens elements 724 a-d mayexhibit a hemispherical shape. The lens elements 724 a-d may thus focusthe illumination respectively provided by the LEDs 706 a-b and 708 a-bon the skin of an individual wear a heart rate monitor that incorporatesthe detection module. As an example, the lens elements 724 a and 724 cmay focus the illumination from the respective near-field LEDs 706 a and706 b such that the amount of illumination reflected of the skin of theindividual and returned to the photodiode 702 is maximized when the skinis at a distance of about 2.8 mm from the face of the detection module700. As another example, the lens elements 724 b and 724 d may focus theillumination from the respective far-field LEDs 708 a and 708 b suchthat the amount of illumination reflected of the skin of the individualand returned to the photodiode 702 is maximized when the skin is at adistance of about 5.6 mm from the face of the detection module 700. Asalso shown by way of example in FIG. 7B, the lens element 722 mayexhibit a cylindrical shape. The lens element 722 may thus serve as alight pipe utilizing total internal reflection to capture illuminationreflected off the skin of an individual and returned to the photodiode702 even when the illumination may be off-center relative to the lenselement.

The lens elements 722 and 724 a-d may be formed of thermoplastic epoxyin a transfer mold process. Slots 726 may separate the respective areasaround the illumination detector 702, the source modules 704 a and 704b, and the microprocessor 710. The slots 726 function to provide a spaceinto which an optically opaque thermoplastic elastomer covering can beformed. In FIG. 7C, the detection module 700 is shown with an opticallyopaque thermoplastic elastomer covering 728 attached. The covering 728includes openings to expose the lens elements 722 and 724 a-d.

The heart rate monitor provided in this disclosure may be well-suitedfor use in wrist-worn portable devices such as sport watches, activitymonitors, portable media players, and other types of device worn by anindividual. The optical heart rate monitor may also be well-suited fordevices where low power consumption is desired and where a determinationof heart rate via electrocardiography is unavailable or otherwise notdesired.

One such device for which the heart rate monitor is well suited includesthe wrist-worn device 800 shown in FIG. 8. A heart rate monitor such asthose described above may be incorporated into the wrist-worn device800. The heart rate monitor may be located in the wrist-worn device 800such that the face of the detection module of the heart rate monitorfaces the skin of an individual when the individual is wearing thewrist-worn device. In some example implementations, the heart ratemonitor may be located at the underside 802 of the wrist-worn device 800near the top of the wrist-worn device such that the face of thedetection module faces downward toward the top of the wrist of theindividual. Other locations for the heart rate monitor may beselectively employed.

The wrist-worn device 800 may include an input mechanism, such as adepressible input button 804 to assist in operation of the device. Theinput button 804 may be operably connected to a controller 806 or otherelectronic components, such as one or more of the elements discussedbelow with reference to FIGS. 9-11. The controller 806 may be embeddedor otherwise part of housing 808. The housing 808 may be formed of oneor more materials, including elastomeric components and comprise one ormore displays, such as display 810. The display 810 may be considered anilluminable portion of the wrist-worn device 800. The display 810 mayinclude a series of individual lighting elements or light members suchas LED lights. The lights may be formed in an array and operablyconnected to the controller 806. The wrist-worn device 800 may includean indicator system 812, which may also be considered a portion orcomponent of the overall display 810. The indicator system 812 mayoperate and illuminate in conjunction with the display 810 (which mayhave multiple pixel members 814) or completely separate from the display810. The indicator system 812 may also include a plurality of additionallighting elements or lighting members 816, which may also take the formof LED lights in one example implementation. In some exampleimplementations, the indicator system 812 may provide a visualindication of goals, such as by illuminating a portion of lightingmembers 816 to represent accomplishment towards one or more goals.

A fastening mechanism 818 can be disengaged wherein the wrist-worndevice 800 can be positioned around a wrist or other portion of anindividual. Once positioned on the individual, the fastening mechanism818 may be subsequently placed in an engaged position. In some exampleimplementations, the fastening mechanism 818 may comprise an interface,including but not limited to a USB port, for operative interaction witha computer or other devices, such as devices. In some exampleimplementations, the fastening member may comprise one or more magnets.In some example implementations, the fastening member may be devoid ofmoving parts and rely entirely on magnetic forces.

In some example implementations, the wrist-worn device 800 may comprisea sensor assembly (not shown). The sensor assembly may comprise aplurality of different sensors, including those disclosed herein orknown in the art. In an example implementation, the sensor assembly maycomprise or permit operative connection to any sensor disclosed hereinor known in the art. The wrist-worn device 800 may be configured toreceive data obtained from one or more external sensors as well. Thewrist-worn device 800 may be configured to display data expressed interms of activity points or currency earned by an individual based onthe activity of the individual.

Referring now to FIG. 9, an example of a personal training system 900.The system 900 may include one or more electronic devices, such ascomputer 902. The computer 902 may comprise a mobile terminal, such as atelephone, music player, tablet, netbook or any portable device. In someexample implementations, the computer 902 may comprise a media player orrecorder, desktop computer, server(s), a gaming console, such as forexample, a Microsoft® XBOX, Sony® Playstation, or a Nintendo® Wii gamingconsoles. It will be appreciated that these are merely example devicesfor descriptive purposes and this disclosure is not limited to anyparticular console or type of computing device.

Turning briefly to FIG. 10, the computer 902 may include a computingunit 904, which may comprise at least one processor unit 906. Processorunit 906 may be any type of processing device configured to executesoftware instructions, such as for example, a microprocessor device. Thecomputer 902 may include a variety of non-transitory computer readablemedia, such as memory 908. The memory 908 may include, but is notlimited to, random access memory (RAM) such as RAM 910; or read onlymemory (ROM), such as ROM 912. The memory 908 may include any one ormore of: electronically erasable programmable read only memory (EEPROM),solid-state memory, optical or magnetic disk storage, or any othernon-transitory medium that can be used to store electronic information.

The processor unit 906 and the memory 908 may be connected, eitherdirectly or indirectly, through a bus 914 or alternate communicationstructure to one or more peripheral devices. For example, the processorunit 906 or memory 908 may be directly or indirectly connected toadditional memory storage, such as hard disk drive 916, optical drive918 or any other memory. The processor unit 906 and memory 908 also maybe directly or indirectly connected to one or more input devices 920 andone or more output devices 922. The output devices 922 may include, forexample, a display device 936 (FIG. 9), audio-visual equipment, tactilefeedback mechanisms or other devices. In some example implementations,one or more display devices may be incorporated into eyewear andoptionally configured to provide feedback to users. The input devices920 may include, for example, a keyboard, touch screen, remote controlpad, pointing device (such as a mouse, touchpad, stylus, trackball, orjoystick), scanner, a camera, a microphone or any sensor disclosedherein. Example sensors and illustrative uses thereof are providedbelow. In this regard, input devices 920 may comprise one or moresensors configured to sense, detect, or measure athletic movement from auser, such as user 924, shown in FIG. 9.

Looking again to FIG. 9, image-capturing device 926 or sensor 928 may beutilized in detecting or measuring athletic movements of user 924. Insome example implementations, data obtained from image-capturing device926 or other sensors, such as sensor 928, may detect athletic movements,either directly (e.g., data may be directly correlated to a motionparameter) or indirectly (data may be utilized in combination, eitherwith each other or with other sensors to detect or measure movements).Thus, certain measurements may be determined from combining dataobtained from two or more devices. The computer 902 may also use touchscreens or image capturing device to determine where a user is pointingto make selections from a graphical user interface. The image-capturingdevice 926 or sensor 928 may include or be operatively connected to oneor more sensors, including but not limited to those disclosed herein.

The computer 902, the computing unit 904, or other electronic devicesmay be directly or indirectly connected to one or more networkinterfaces, such as example interface 930 (as shown in FIG. 10)configured to permit communication with a network, such as network 932(FIG. 9). In the example of FIG.10, the network interface 930, maycomprise a network adapter or network interface card (NIC) configured totranslate data and control signals from the computing unit 904 intonetwork messages according to one or more communication protocols, suchas the Transmission Control Protocol (TCP), the Internet Protocol (IP),and the User Datagram Protocol (UDP). The network interface 930 mayemploy any suitable connection agent for connecting to a network 932.The network 932, however, may be any one or more informationdistribution network(s), of any type(s) or topology(s), alone or incombination(s), such as internet(s), intranet(s), cloud(s), LAN(s). Thenetwork 932 may be any one or more of cable, fiber, satellite,telephone, cellular, wireless, etc. and as such, be variously configuredsuch as having one or more wired or wireless communication channels(including but not limited to: WiFi®, Bluetooth®, or ANT technologies)to connect one or more locations (e.g., schools, businesses, homes,consumer dwellings, network resources, etc.), servers 934, or to otherdevices, which may be similar or identical to the computer 902. Indeed,the system 900 may include more than one instance of each component(e.g., more than one computer 902, more than one display 936, and soforth).

Regardless of whether the computer 902 (or other device within thenetwork 932) is portable or at a fixed location, it should beappreciated that, in addition to the input, output and storageperipheral devices specifically listed above, the computing device maybe connected, such as either directly, or through the network 932 to avariety of other peripheral devices. In some example implementations, asingle device may integrate one or more components shown in FIG. 9. Forexample, a single device may include the computer 902, image-capturingdevice 926, sensor 928, display 936 and additional components. In someexample implementations, the sensor device 938 may comprise a mobileterminal having a display 936, image-capturing device 926, and one ormore sensors 928. In other example implementations, the image-capturingdevice 926 or sensor 928 may be peripherals configured to be operativelyconnected to a media device, including for example, a portable gaming ormedia system.

Sensors, such as sensors 926 and 928, may be configured to detect ormonitor at least one fitness parameter of a user 924. The sensors 926and 928 may include, but are not limited to: an accelerometer, agyroscope, a location-determining device (e.g., GPS), light (includingnon-visible light) sensor, temperature sensor (including ambienttemperature or body temperature), sleep pattern sensors, heart ratemonitor, image-capturing sensor, moisture sensor, force sensor, compass,angular rate sensor, or combinations thereof. The network 932 or thecomputer 902 may be in communication with one or more electronic devicesof system 900, including for example, the display 936, an imagecapturing device 926 (e.g., one or more video cameras), and sensor 928,which may be an infrared (IR) device. In one example implementation, thesensor 928 may comprise an IR transceiver. For example, the sensors 926and 928 may transmit waveforms into the environment, including towardsthe direction of the user 924 and receive a “reflection” or otherwisedetect alterations of those released waveforms. In some exampleimplementations, sensors may be passive, such as reflective materialsthat may be detected by image-capturing device 926 or sensor 928 (amongothers). In other example implementations, the image-capturing device926 or sensor 928 may be configured to transmit or receive otherwireless signals, such as radar, sonar, or audible information. It willbe appreciated that signals corresponding to a multitude of differentdata spectrums may be utilized in accordance with variousimplementations. In this regard, the sensors 926 and 928 may detectwaveforms emitted from external sources other than the system 900. Forexample, the sensors 926 and 928 may detect heat being emitted from theuser 924 or the surrounding environment. Thus, the image-capturingdevice 926 and the sensor 928 may comprise one or more thermal imagingdevices. In one example implementation, the image-capturing device 926and the sensor 928 may comprise an IR device configured to perform rangephenomenology. As an example, image-capturing devices configured toperform range phenomenology are commercially available from FlirSystems, Inc. of Portland, Oreg. Although the image capturing device926, the sensor 928, and the display 936 are shown in direct (wirelesslyor wired) communication with computer 902, it will be appreciated thatthese devices may directly communicate (wirelessly or wired) with thenetwork 932.

Detected movements or parameters from any sensor(s) disclosed herein mayinclude (or be used to form) a variety of different parameters, metricsor physiological characteristics including but not limited to speed,acceleration, distance, steps taken, calories, heart rate, sweatdetection, effort, oxygen consumed, oxygen kinetics, angular rate,pressure, direction, rotational forces, impact forces, and combinationsthereof. Such parameters may also be expressed in terms of activitypoints or currency earned by the user based on the activity of the user.

As seen in FIG. 9, the user 924 may possess, carry, or wear any numberof devices, including sensory devices 938, 940, 942, or 944. One or moreof the devices 938, 940, 942, or 944 may not be specially manufacturedfor fitness or athletic purposes. Indeed, aspects of this disclosurerelate to utilizing data from a plurality of devices, some of which arenot fitness devices, to collect, detect, or measure athletic data. Inone example implementation, the device 938 may comprise a portableelectronic device, such as a telephone or digital music player,including an IPOD®, IPAD®, or iPhone®, brand devices available fromApple, Inc. of Cupertino, Calif. or Zune® or Microsoft® Windows devicesavailable from Microsoft of Redmond, Washington. It will be recognizedthat digital media players can serve as an output device, input device,or storage device for a computer. In some example implementations, thedevice 938 may be the computer 902, yet in other exampleimplementations, the computer 902 may be entirely distinct from thedevice 938. Regardless of whether the device 938 is configured toprovide certain output, it may serve as an input device for receivingsensory information. The devices 938, 940, 942, or 944 may include oneor more sensors, including but not limited to any sensor known in theart or disclosed herein.

The devices 938-944 may communicate with each other, either directly orthrough a network, such as network 932. Communication between one ormore of the devices 938-944 may take place via the computer 902. Forexample, two or more of the devices 938-944 may be peripheralsoperatively connected to the bus 914 of the computer 902. In yet anotherexample implementation, a first device, such as the device 938 maycommunicate with a first computer, such as the computer 902 as well asanother device, such as the device 942, however, the device 942 may notbe configured to connect to computer 902 but may communicate with thedevice 938. It will be appreciated that other configurations arepossible. Also, the components shown in FIG. 10 may be included in theserver 934, other computers, apparatuses, and so forth.

In some example implementations, the sensory devices 938, 940, 942 or944 may be formed within or otherwise associated with the clothing ofthe user 924 or accessories of the user, including a watch, armband,wristband, necklace, shirt, shoe, or the like. Examples of wrist-worndevices (e.g., wrist-worn device 800) were described above, however,these are merely example implementations and this disclosure should notbe limited to such. These devices may be configured to monitor athleticmovements of a user, including all-day activity of the user 924. Thedevices may detect athletic movement when the user 924 interacts withthe computer 902 or operate independently of the computer 902. Forexample, each device may be configured to function as an-all dayactivity monitor that measures activity regardless of the proximity ofthe user 924 to or interactions with the computer 902.

In some example implementations, sensors, such as the sensors 944 shownin FIG. 9, may be integrated into apparel, such as athletic clothing.For instance, the user 924 may wear one or more on-body sensors 944 a-b.The sensors 944 may be incorporated into the clothing of the user 924 orplaced at any desired location of the body of user 924. The sensors 944may communicate (e.g., wirelessly) with the computer 902; the sensors928, 938, 940, and 842; or the camera 926. Examples of interactivegaming apparel are described in U.S. patent application Ser. No.10/286,396, filed Oct. 30, 2002, and published as U.S. Pat. Pub, No.2004/0087366, which is incorporated by reference herein in its entirety.In some example implementations, passive sensing surfaces may reflectwaveforms, such as infrared light, emitted by the image-capturing device926 or the sensor 928. In one example implementation, passive sensorslocated on apparel of the user 924 may comprise generally sphericalstructures made of glass or other transparent or translucent surfaceswhich may reflect waveforms. Different classes of apparel may beutilized in which a given class of apparel has specific sensorsconfigured to be located proximate to a specific portion of the body ofthe user 924 when properly worn. For example, golf apparel may includeone or more sensors positioned on the apparel in a first configurationand yet soccer apparel may include one or more sensors positioned onapparel in a second configuration.

FIG. 11 shows illustrative locations for sensory input (e.g., sensorylocations 946 a-946 o). In this regard, sensors may be physical sensorslocated on or in the clothing of a user in some example implementations.In example implementations, the sensor locations 946 a-946 o may bebased upon identification of relationships between two moving bodyparts. For example, sensor location 946 a may be determined byidentifying motions of the user 924 with an image-capturing device, suchas image-capturing device 926. Thus, in some example implementations, asensor may not physically be located at a specific location (such assensor locations 946 a-946 o), but is configured to sense properties ofthat location, such as with image-capturing device 926 or other sensordata gathered from other locations. In this regard, the overall shape orportion of the body of the user 924 may permit identification of certainbody parts. Regardless of whether an image-capturing device, such ascamera 926, is utilized or a physical sensor located on the user 924, orusing data from other devices, the sensors may sense a current locationof a body part or track movement of the body part. In one exampleimplementation, sensory data relating to location 946 m may be utilizedin a determination of the center of gravity (i.e., center of mass) ofthe user 924. For example, relationships between the sensor location 946a and the sensor locations 946 f or 946 l with respect to one or more ofthe sensor locations 946 m-946 o may be utilized to determine if thecenter of gravity has been elevated along the vertical axis (such asduring a jump) or if a user is attempting to “fake” a jump by bendingand flexing their knees. In one example implementation, the sensorlocation 946 n may be located at about the sternum of the user 924.Likewise, the sensor location 946 o may be located approximate to thenaval of user 924. In some example implementations, data from the sensorlocations 946 m-946 o may be utilized (alone or in combination withother data) to determine the center of gravity for the user 924. In someexample implementations, relationships between multiple several sensorlocations, such as sensor locations 946 m-946 o, may be utilized indetermining orientation of the user 924 or rotational forces, such astwisting of the torso of the user 924. Further, one or more sensorlocations may be utilized to determine a center of moment location. Forexample, one or more of the sensor locations 946 m-946 o may serve as apoint for a center of moment location of the user 924. In anotherexample implementations, one or more of the sensor locations may serveas a center of moment of specific body parts or regions.

Further aspects of this disclosure relate to determinations of when auser, such as the user 924, is active or inactive. Some exampleimplementations may relate to altering electronic outputs, such asrewards (e.g., rewarding or deducting virtual or physical awards), basedupon activity levels. In this regard, determinations of activity orinactivity may be utilized as an adjustment criterion. For example,energy expenditure values may be determined and energy expenditurepoints may be deducted when the user 924 has been inactive for apredetermined period of time or enhanced when certain criteria are met.This feature may be included with all calculations or may be used invarious games and competitions. For example, it may be determinedwhether an adjustment criterion has been met. The adjustment criterionmay include inactivity for a predetermined time period. In some exampleimplementations inactivity is not determined by merely determining thatan amount of time has passed since with user was active.

When an adjustment criterion has been met, a reward, such as forexample, energy expenditure points, may be adjusted. The adjustment maybe a function of a property of the detected inactivity (e.g., duration,intensity, type, threshold, specific biometric or physiologicalparameter, etc.). In some example implementations, a device or alarm mayinform the user 924 (or authorized groups/individuals) that the user:(a) may be close to receiving a reduction in an award, such as energyexpenditure points, to encourage activity; or (b) that user received areduction of energy expenditure points. Thus, teammates or competingusers may be notified of a reduction (or potential for reduction), andteachers, trainers, or parents may more readily monitor the physicalactivity of others. In some example implementations, a device, such asdevice 800 (FIG. 8), or any other device disclosed herein, may beconfigured to sense activity levels and detect that the user has been ina non-active (e.g., low activity) state for a predetermined amount oftime, and in response, transmit an alert message to a local or remoteoutput device to remind the user to become more active.

The property of the detected inactivity (duration, intensity, etc.) maybe conducted at various intervals and allow for tracking pointsconcurrently for different time periods, such as days, weeks and years.The threshold levels of a low activity state and amount of inactive timecould also vary and be individually set by the user 924 or any otherindividual or group.

In some arrangements, user non-activity or inactivity may also bedetected and affect progress toward completion of an activity goal. Forexample, inactivity may be detected when a user does not exhibitmovement of a particular level or a type of movement for a specifiedamount of time, does not exhibit a heart rate of at least a thresholdlevel, does not move a sufficient amount of distance over an amount oftime and the like or combinations thereof. For arrangements in which auser accumulates activity points to reach an activity point goal, pointsor a value may be deducted from the activity points or other activitymetric total when an amount of non-activity (e.g., inactivity orsedentary state) is detected. Various conversion rates for convertinginactivity to activity point deductions may be used. In one example, 10minutes of inactivity may correspond to a 5 point deduction. In anotherexample, 30 minutes of inactivity may correspond to a 100 pointdeduction. Loss or deduction of activity points may be linear or may benon-linear, for example, exponential, parabolic and the like.

Non-active time may include inactive time and sedentary time. Inactivityand sedentary time may be defined by different movement, heart-rate (orother physiological parameter), step or other thresholds or may bedefined using the same thresholds. In one example, sedentary time mayhave a higher threshold (e.g., requiring a higher level of activity)than an inactivity threshold. That is, an individual may be consideredsedentary but not inactive. The non-active threshold may correspond tothe sedentary threshold or a higher threshold, if desired.Alternatively, an inactivity threshold may be greater than a sedentarythreshold. There may also be multiple sedentary thresholds, inactivitythresholds or non-active thresholds (e.g., each of the sedentary andinactivity thresholds may be a non-active threshold). Different pointdeductions or rates of point deductions may also be defined between themultiple thresholds and levels of little to no activity (e.g.,non-activity). For example, a user may lose 50 points per hour forinactivity and 30 points per hour for sedentary activity or vice versa.Further, activity point deduction may be triggered at different timesdepending on if the user is inactive or sedentary. For instance, a usermay begin losing activity points after 30 minutes of inactivity or 45minutes of being sedentary. Additional thresholds (e.g., more than twothresholds) and corresponding rates of activity point loss may also bedefined.

In some arrangements, various sensors may be used to detect non-activeperiods of time. As discussed, non-activity time periods may be definedbased on heart-rate, amplitude of a movement signal, step rate (e.g.,<10 steps per minute), or the like. Alternatively or additionally,inactivity and sedentary time periods may be measured based on aphysical position, body position, body orientation, body posture of ortype of activity being performed by the individual. The detrimentaleffects of various physical inactivity or sedentary body positions ororientations may also differ. Accordingly, 30 minutes of reclining mayintroduce the same health risks as 45 minutes of sitting. The potentialfor health risks may also be time-dependent. Accordingly, non-activity(e.g., sleeping) for a specified range of durations and during aspecified range of time might not introduce health risks. In oneexample, sleeping for 7-9 hours between 9 PM and 9 AM might notintroduce detrimental health risks and thus, might not contribute toactivity point or other activity metric value deduction. Indeed, in someexample, a lack of inactivity (such as sleep) for a specified range ofdurations or during a specified range of time may be considereddetrimental to the health of a user. Thus, activity points may bededucted or activity points may be accumulated at a slower rate duringthese times.

Additionally or alternatively, the amount by which a value of theactivity metric (e.g., an activity points) is decreased may bedetermined based on time of day, location of the user, physical positionof the user, level of inactivity and the like. For example, a user maylose greater value in an activity metric or at a faster rate during theafternoon than during the evenings. In another example, if a user is ata gym, the user may lose fewer activity points or other activity metricor lose value in the metric at a slower rate than if the user waslocated at home.

To account for the variances in types of non-active activity (e.g.,below a requisite level of movement to be considered activity), a systemmay distinguish between physical body positions or orientationsincluding, for example, sleeping, reclining, sitting and standing.Distinguishing between different physical body positions andorientations may be determined from sensors at different locations ofthe body of the user (or sensors configured to detect locations ofcertain body parts). The physical body position of the user may then bedetermined based on the relative positions of the body parts to oneanother. For example, when a knee location sensor is within a firstthreshold distance of a waist or chest sensor, the system may determinethat the user is sitting. If the knee location sensor is outside of thefirst threshold distance, the system may determine that the user isstanding. In other examples, an angle formed by the various sensors maybe used to determine an individual's position. Additionally oralternatively, the location of the various body parts of a user may beevaluated in conjunction with accelerometer or movement data todetermine if the user is exhibiting movement or (e.g., at, above orbelow) a specified level of movement.

In addition to deductions in activity points, the system may alert auser to inactivity to encourage active lifestyles. In one example, thesystem may alert the user (or authorized individuals or groups) bydisplaying a message or indicator on a device, such as any devicedescribed herein, after a specified amount of inactivity such as 2minutes, 5 minutes, 30 minutes, 1 hour and the like. The amount ofinactivity time may be additive over non-consecutive time periods. Anamount of consecutive inactivity time may alternatively or additionallybe tracked. For example, if the user is inactive between 10:15 and 11:00AM and then again between 2:00 and 2:30 PM, the total amount ofnon-active time may be 1 hour and 15 minutes. The message or indicatorof inactivity may be provided as a warning prior to deducting activitypoints. For example, the message may indicate that X amount of activitypoints will be deducted if the user does not exhibit a sufficient levelof activity within a specified amount of time (e.g., 30 minutes, 5minutes, 10 seconds, 30 seconds, 1 hour, 2 hours, etc.). Accordingly,the device may include a non-active timer to determine the amount ofuser non-activity. Additionally, the message may provide a suggestion asto a type of activity the user should perform to counter any risksintroduced by the inactivity. For example, the system may suggest thatthe user walk 1 hour at a 10 minute mile pace. When the user hascounteracted or accounted for the risks or negative effects of thedetected amount of inactivity time, a celebratory message or otherindication may be provided.

Warnings, point deductions, or other notifications may be provided if auser returns to a sedentary or a non-active mode within a specifiedamount of time of exiting sedentary or a non-active mode. For example,the user may exercise or exhibit a sufficient level of activity to exitthe sedentary or a non-active mode for a period of 10 minutes. However,the system or device may require at least 30 minutes of activity toavoid additional warnings for a period of time such as 1 hour, 2 hours,3 hours, etc. For example, the warnings may indicate that the user didnot exhibit activity for a sufficient amount of time or a sufficientlevel of activity or a combination thereof. Additionally, multiplesedentary periods within short amounts of time (e.g., a threshold amountof time) may require higher or additional levels of activity tocounteract potential sedentary effects including health risks and thelike. In a particular example, the user may be required to perform ahigher level of activity to halt point deduction.

The device or other system may further advise a user as to an amount ofnon-active time allowed before negative health effects may occur. In oneexample, the device or system may include a countdown indicating aremaining amount of allowable non-active time before potential healthrisks may begin taking effect. An amount of permissible non-active timemay be earned or accumulated based on an amount of activity performed.Accordingly, the device may also provide suggestions or recommendationsas to a type or duration of activity that may be performed to earn aspecified amount of non-active time (e.g., 1 hour of TV watching).Different types of non-active or sedentary activities may requiredifferent types or amounts of activity. For example, 1 hour of recliningmay require more strenuous or longer exercise than 1 hour of sitting. Inanother example, 1 hour of sitting while knitting may require lessstrenuous or a lower amount of exercise or activity than 1 hour ofsitting while watching television. According to one or morearrangements, recommendations may be generated based on empirical dataor predefined programming and data tables specifying a type or durationof activity and a corresponding amount of permissible non-activity.

The device or activity tracking system may further recommend activitiesbased on historical records. For instance, the device or tracking systemmay determine activity performed by the user in the past and generaterecommendations based on those types of activities. Additionally oralternatively, the device or tracking system may generaterecommendations for specific workouts performed by the user in the past.For example, a user may need to perform 500 calories worth of activityto counteract 2 hours of TV watching. In such a case, the system mayrecommend a particular workout performed by the user in the past inwhich the user burned 500 calories. Combinations of historical activitytypes and specific historical workouts may be used to generaterecommendations. In one example, the system may recommend one of twoworkouts that the user has performed in the past based on a type ofworkout that the user appears to prefer. The preference may bedetermined based on a number of times the user has performed each typeof workout. A workout or activity type may also be recommended based onlocation and time. For example, if a user previously performs aparticular type of activity or a particular workout routine at the samelocation or at the same time, the system may recommend that type ofactivity or workout routine. Other recommendations algorithms andfactors may be used.

The system 900 (FIG. 9) may be configured to transmit energy expenditurepoints to a social networking website. The users may be ranked based ontheir total number of points for a desired time interval (e.g., rank byday, week, month, year, etc.).

Aspects of the disclosure have been described in terms of illustrativeembodiments thereof. Numerous other embodiments, modifications andvariations within the scope and spirit of the appended claims will occurto persons of ordinary skill in the art from a review of thisdisclosure. For example, one of ordinary skill in the art willappreciate that the steps illustrated in the illustrative figures may beperformed in other than the recited order, and that one or more stepsillustrated may be optional in accordance with aspects of thedisclosure.

What is claimed is:
 1. A method of determining heart rate, the methodcomprising: (a) illuminating skin of a user with an illumination source,the illumination source comprising a near-field illumination source anda far-field illumination source wherein the near-field illuminationsource comprises a first lens element configured to focus firstelectromagnetic radiation provided by the near-field illumination sourcesuch that the first electromagnetic radiation achieves maximumreflection with the skin positioned a first distance from anillumination detector and wherein the far-field illumination sourcecomprises a second lens element configured to focus secondelectromagnetic radiation provided by the far-field illumination sourcesuch that the second electromagnetic radiation achieves maximumreflection with the skin positioned a second distance, greater than thefirst distance, from the illumination detector; (b) detectingelectromagnetic radiation reflected off the skin of the user with theillumination detector, the electromagnetic radiation detected comprisinga first amount, N, of electromagnetic radiation provided by thenear-field illumination source and a second amount, F, ofelectromagnetic radiation provided by the far-field illumination source;(c) determining a position of the skin of the user relative to theillumination detector based on the electromagnetic radiation reflectedwherein determining the position comprises calculating a ratio of thefirst amount of electromagnetic radiation reflected and the secondamount of electromagnetic radiation reflected; and (d) determining, at aprocessor, a heart rate of the user wherein determining the heart ratecomprises analyzing information corresponding to the electromagneticradiation reflected and compensating for the position of the skin of theuser.
 2. The method of claim 1, wherein the illumination sourcecomprises at least one light-emitting diode (LED).
 3. The method ofclaim 2 wherein the at least one LED is configured to generate infrared(IR) illumination.
 4. The method of claim 1 wherein the illuminationdetector comprises a photodiode.
 5. The method of claim 1 wherein theratio is equal to N/F.
 6. The method of claim 1 wherein: step (c)comprises accessing a lookup table that associates skin positions withrespective compensation factors; and step (d) includes receiving acompensation factor associated with the position of the skin of the userand utilizing the compensation factor when determining the heart rate ofthe user.
 7. A heart rate determination system comprising: a processor;an illumination source configured to illuminate skin of a user, theillumination source comprising a near-field illumination source and afar-field illumination source; an illumination detector that detectselectromagnetic radiation reflected off the skin of the user, theelectromagnetic radiation detected comprising a first amount, N, ofelectromagnetic radiation provided by the near-field illumination sourceand a second amount, F, of electromagnetic radiation provided by thefar-field illumination source; a first lens element configured to focusfirst electromagnetic radiation provided by the near-field illuminationsource such that the first electromagnetic radiation achieves maximumreflection with the skin positioned a first distance from theillumination detector; a second lens element configured to focus secondelectromagnetic radiation provided by the far-field illumination sourcesuch that the second electromagnetic radiation achieves maximumreflection with the skin positioned a second distance, greater than thefirst distance, from the illumination detector; and memory storinginstructions that, when executed by the processor, cause the processorto: determine a position of the skin of the user relative to theillumination detector, and determine a heart rate of the user byanalyzing information corresponding to an amount of the electromagneticradiation detected by the illumination detector and compensating for theposition of the skin of the user.
 8. The heart rate determination systemof claim 7 wherein the near-field illumination source comprises anear-field light-emitting diode (LED) and the far-field illuminationsource comprises a far-field light-emitting diode.
 9. The heart ratedetermination system of claim 8 wherein: the instructions, when executedby the processor, further cause the processor to determine acompensation factor based on a ratio of the first amount ofelectromagnetic radiation, N, to the second amount of electromagneticradiation, F.
 10. The heart rate determination system of claim 9 furthercomprising: a lookup table that associates skin positions withrespective compensation factors; and the instructions, when executed bythe processor, further cause the processor to perform a lookup at thelookup table using the ratio and provide a compensation factorassociated with the ratio to the processor.
 11. The heart ratedetermination system of claim 8 wherein the illumination source is afirst illumination source, the near-field LED is a first near-field LED,and the far-field LED is a first far-field LED and further comprising: asecond illumination source that comprises a second near-field LED and asecond far-field LED.
 12. The heart rate determination system of claim11 wherein the first illumination source and the second illuminationsource are positioned substantially orthogonal to each other.
 13. Theheart rate determination system of claim 11 wherein: the firstnear-field LED is positioned between the illumination detector and thefirst far-field LED; and the second near-field LED is positioned betweenthe illumination detector and the second far-field LED.
 14. The heartrate determination system of claim 7 wherein the illumination detectorcomprises a photodiode.
 15. The heart rate determination system of claim7 wherein the heart rate determination system is incorporated into awrist-worn device that is configured to measure movements of anindividual wearing the wrist-worn device.